Optical protection switch with broadcast multi-directional capability

ABSTRACT

An apparatus includes a first reconfigurable optical add/drop multiplexer (ROADM) to receive a first optical signal and a second ROADM to receive a second optical signal. The apparatus also includes a reconfigurable optical switch that includes a first switch, switchable between a first state and a second state, to transmit the first optical signal at the first state and block the first optical signal at the second state. The reconfigurable optical switch also includes a second switch, switchable between the first state and the second state, to transmit the second optical signal at the first state and block the second optical signal at the second state. The reconfigurable optical switch also includes an output port to transmit an output signal that is a sum of possible optical signals transmitted through the first switch and the second switch.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Division of U.S. patent application Ser. No.15/721,804, filed Sep. 30, 2017, and entitled “Optical Protection SwitchWith Broadcast Multi-Directional Capability,” the disclosure of which isincorporated herein by reference in its entirety.

FIELD

One or more embodiments relate to methods and apparatus of opticalprotection switching with broadcast capability.

BACKGROUND

Telecommunication networks usually use one or more end-to-end protectionschemes to protect against potential failures on service providers'network(s) that might affect the services offered to end customers. Inan optical telecommunication network, one protection scheme is the 1+1protection scheme, in which a head-end optical splitter is used to splitan optical signal and send duplicated copies of the optical signal intotwo paths (usually referred to as primary path and secondary path) fordiverse path routing. The conventional 1+1 protection scheme alsoemploys a tail-end optical switch (e.g., a 2×1 optical switch) connectedto the two paths to select the copy of the optical signal from eitherthe primary path or the secondary path. For example, if the opticalnetwork detects that the signal from the primary path is unsatisfactory(e.g., the signal power is lower than a threshold value), the secondarypath is then used for communication. In this scheme, the tail-endoptical switch, also referred to as the optical protection switch, canonly select one path or the other, but not both.

In optical networks using reconfigurable optical add/drop multiplexers(ROADMs), additional degrees of freedom are introduced as the opticalmultiplexing may also be multi-stage. For example, a group of channelscan be multiplexed into one single fiber employed as the primary pathand another single fiber employed as the secondary path. In this case,optical protection can be applied to the whole group of optical channelsby inserting the optical protection switch between the primary andsecondary multiplexers. The optical protection switch, however, usuallycan only switch the entire group and lacks the flexibility formulti-direction multiplexing. In other words, existing approachesusually can only receive the group of protected channels from onedirection or the other. Some other multi-direction multiplexerapproaches, in contrast, may allow for channels to be configured asnon-protected services, but still share a single common mux/demux port.

SUMMARY

Some embodiments described herein relate generally to optical protectionswitching with broadcast capability, and, in particular, to methods andapparatus for optical protection switching by replacing 2×1 opticalswitches in an optical network with 2 or more 1×1 optical switches.

In some embodiments, an apparatus includes a first reconfigurableoptical add/drop multiplexer (ROADM) configured to receive a firstoptical signal on a first optical channel and a second ROADM configuredto receive a second optical signal on a second optical channel. Theapparatus also includes a reconfigurable optical switch that includes afirst switch, in optical communication with the first ROADM andswitchable between a first state and a second state, to transmit thefirst optical signal at the first state and block the first opticalsignal at the second state. The reconfigurable optical switch alsoincludes a second switch, in optical communication with the second ROADMand switchable between the first state and the second state, to transmitthe second optical signal at the first state and block the secondoptical signal at the second state. The reconfigurable optical switchalso includes an output port, in optical communication with the firstswitch and the second switch, to transmit an output signal that is a sumof possible optical signals transmitted through the first switch and thesecond switch.

In some embodiments, a method includes receiving a first optical signalfrom a first reconfigurable optical add/drop multiplexer (ROADM) andtransmitting the first optical signal to a first switch in opticalcommunication with the first ROADM. The first optical switch isswitchable between a first state and a second state. The first switch isconfigured to transmit the first optical signal at the first state andblock the first optical signal at the second state. The method alsoincludes receiving a second optical signal from a second ROADM andtransmitting the second optical signal to a second switch in opticalcommunication with the second ROADM. The second switch is switchablebetween the first state and the second state. The second switch isconfigured to transmit the second optical signal at the first state andblock and second optical signal at the second state. The method alsoincludes generating an output signal that is a sum of possible opticalsignals transmitted through the first switch and the second switch.

In some embodiments, an optical network includes a first node, a secondnode, and a third node. The first node includes a first transceiver totransmit a first optical signal, a first reconfigurable optical add/dropmultiplexer (ROADM) operatively coupled to the first transceiver, and afirst switch disposed between the first ROADM and the first transceiver.The first node also includes a second ROADM operatively coupled to thefirst transceiver and a second switch disposed between the second ROADMand the first transceiver. The second node includes a second transceiverto transmit a second optical signal, a third ROADM operatively coupledto the second transceiver and configured to receive the first opticalsignal from the first node, and a third switch disposed between thethird ROADM and the second transceiver. The second node also includes afourth ROADM operatively coupled to the second transceiver and a fourthswitch disposed between the fourth ROADM and the second transceiver. Thethird node includes a third transceiver to transmit a third opticalsignal, a fifth ROADM operatively coupled to the third transceiver andconfigured to receive the first optical signal from the first node, anda fifth switch disposed between the fifth ROADM and the thirdtransceiver. The third node also includes a sixth ROADM operativelycoupled to the third transceiver and configured to receive the secondoptical signal from the second node and a sixth switch disposed betweenthe sixth ROADM and the third transceiver. The optical network alsoincludes a controller, operatively coupled to the first node, the secondnode, and the third node, to control the first switch, the secondswitch, the third switch, the fourth switch, the fifth switch, and thesixth switch.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings primarily are for illustrative purposes and are notintended to limit the scope of the subject matter described herein. Thedrawings are not necessarily to scale; in some instances, variousaspects of the subject matter disclosed herein may be shown exaggeratedor enlarged in the drawings to facilitate an understanding of differentfeatures. In the drawings, like reference characters generally refer tolike features (e.g., functionally similar and/or structurally similarelements).

FIG. 1 shows a schematic of an apparatus reconfigurable between anoptical protection switch and a broadcast switch, according to someembodiments.

FIG. 2 shows a schematic of a reconfigurable optical switch configuredin optical protection mode, according to some embodiments.

FIG. 3 shows a schematic of a reconfigurable optical switch configuredin multi-direction mode, according to some embodiments.

FIG. 4 shows a schematic of a reconfigurable optical switch includingfour switches, according to some embodiments.

FIG. 5 shows a schematic of an optical network including areconfigurable optical switch for optical channel (OCH) protection andmulti-directional multiplexing, according to some embodiments.

FIG. 6 shows a schematic of an optical network including areconfigurable optical switch for optical multiplexing section (OMS)protection and multi-directional multiplexing, according to someembodiments.

FIG. 7 shows a schematic of an optical network including groupmultiplexing and using a reconfigurable optical switch for pathprotection and multi-directional multiplexing, according to someembodiments.

FIG. 8 shows a schematic of an optical network including areconfigurable optical switch for path protection, according to someembodiments.

FIG. 9 shows a schematic of an optical network including areconfigurable optical switch for multi-directional multiplexing,according to some embodiments.

FIGS. 10A and 10B each illustrate a schematic of an optical networkhaving reconfigurability between path protection and multi-directionalmultiplexing of an optical network, according to some embodiments.

FIG. 11 illustrates a method of optical communication includingreconfigurable optical switching, according to some embodiments.

DETAILED DESCRIPTION

In some embodiments, an apparatus includes a first reconfigurableoptical add/drop multiplexer (ROADM) configured to receive a firstoptical signal on a first optical channel and a second ROADM configuredto receive a second optical signal on a second optical channel. Theapparatus also includes a reconfigurable optical switch that includes afirst switch, in optical communication with the first ROADM andswitchable between a first state and a second state, to transmit thefirst optical signal at the first state and block the first opticalsignal at the second state. The reconfigurable optical switch alsoincludes a second switch, in optical communication with the second ROADMand switchable between the first state and the second state, to transmitthe second optical signal at the first state and block the secondoptical signal at the second state. The reconfigurable optical switchalso includes an output port, in optical communication with the firstswitch and the second switch, to transmit an output signal that is a sumof possible optical signals transmitted through the first switch and thesecond switch.

In some embodiments, the first switch and/or the second switch caninclude at least one of a variable optical attenuator (VOA), anelectro-optical switch, an acousto-optical switch, and anopto-mechanical switch.

In some embodiments, the first ROADM is configured to transmit a firstspectral component at a first wavelength and block spectral componentsat other wavelengths. The second ROADM is configured to transmit asecond spectral component at a second wavelength and block spectralcomponents at other wavelengths. The output signal includes the firstspectral component and the second spectral component.

In some embodiments, the first ROADM is configured to transmit a firstgroup of spectral components at a first group of wavelengths (eachspectral component can have a distinct wavelength), the second ROADM isconfigured to transmit a second group of spectral components at a secondgroup of wavelengths (each spectral component can have a distinctwavelength), and the output signal includes the first group of spectralcomponents and the second group of spectral components.

In some embodiments, the apparatus further includes a demultiplexer, inoptical communication with the output port, to direct the first spectralcomponent to a first receiver and the second spectral component into asecond receiver. In some embodiments, the apparatus further includes anoptical splitter to distribute different spectral components todifferent receivers. The apparatus can also use the selectivity ofcoherent detectors (e.g., using a local oscillator) to detect signalfrom each individual spectral component at a distinct wavelength.

In some embodiments, the apparatus also includes a controller,operatively coupled to the first switch and the second switch, tocontrol the apparatus between at least three operation modes: a firstoperation mode, a second operation mode, and a third operation mode. Inthe first operation mode, the first switch is in the first state and thesecond switch is in the second state, in which case the apparatus isused as an optical protection switch. In the second operation mode, boththe first switch and the second switch are configured in the firststate, in which case the apparatus is used for multi-direction broadcastallowing unprotected wavelength operation to have high spectralefficiency usage (see more details below with reference to FIGS. 10A and10B). In the third operation mode, both the first switch and the secondswitch are configured in the second state.

In some embodiments, the apparatus can include more than two ROADMs andaccordingly more than two switches. For example, the number of ROADMscan be 2^(N), where N is a positive integer. In this case, the outputsignal is a sum of possible optical signals transmitted through thesemultiple switches.

In some embodiments, a method includes receiving a first optical signalfrom a first reconfigurable optical add/drop multiplexer (ROADM) andtransmitting the first optical signal to a first switch in opticalcommunication with the first ROADM. The first optical switch isswitchable between a first state and a second state. The first switch isconfigured to transmit the first optical signal at the first state andblock the first optical signal at the second state. The method alsoincludes receiving a second optical signal from a second ROADM andtransmitting the second optical signal to a second switch in opticalcommunication with the second ROADM. The second switch is switchablebetween the first state and the second state. The second switch isconfigured to transmit the second optical signal at the first state andblock the second optical signal at the second state. The method alsoincludes generating an output signal that is a sum of possible opticalsignals transmitted through the first switch and the second switch.

FIG. 1 shows a schematic of an apparatus 100 reconfigurable between anoptical protection switch and a broadcast switch, according to someembodiments. The apparatus 100 includes a first reconfigurable opticaladd/drop multiplexer (ROADM) 110 a to receive a first optical signal 101a and the optical signal transmitted through the first ROADM 110 a isdesignated as 103 a. A second ROADM 110 b is used to receive a secondoptical signal 101 b and the optical signal transmitted through thesecond ROADM 110 b is designated as 103 b. In some embodiments, theoptical signals 101 a and 103 a can be identical, and the opticalsignals 101 b and 103 b can be identical.

A reconfigurable optical switch 140 is included in the apparatus 100 toreceive the two optical signals 103 a and 103 b after the correspondingROADM 110 a and 110 b. More specifically, the first optical signal 103 ais transmitted to a first switch 120 a and the second optical signal 103b is transmitted to a second switch 120 b. Both switches 120 a and 120 bare switchable between a first state and the second state. In the firststate (also referred to as a “pass” state), the switches 120 a and 120 bare configured to pass the optical signal 103 a and 103 b, respectively.In the second state (also referred to as a “block” state), the switches120 a and 120 b are configured to block the optical signals 103 a and103 b, respectively.

The two switches 120 a and 120 b collectively can have four differentconfigurations. In the first configuration, the first switch 120 a is inthe first state to pass the first optical signal 103 a and the secondswitch 120 b is in the second state to block the second optical signal103 b. The output signal 102 then includes only the first optical signal103 a. In the second configuration, the first switch 120 a is in thesecond state to block the first optical signal 103 a and the secondswitch 120 b is in the first state to pass the second optical signal 103b. The output signal 102 then includes only the second optical signal103 b.

In the third configuration, both switches 120 a and 120 b are in thefirst state to pass the optical signals 103 a and 103 b, respectively.In this configuration, the output signal 102 includes a sum of the firstoptical signal 103 a and the second optical signal 103 b. In the fourthconfiguration, both switches 120 a and 120 b are in the second state toblock the optical signals 103 a and 103 b, respectively. In thisconfiguration, the output signal 102 includes neither the first opticalsignal 103 a nor the second optical signal 103 b.

These different configurations of the two switches 120 a and 120 b allowflexible functions of the apparatus 100, which can be used as an opticalprotection switch and/or a multi-direction multiplexer. This providesgreater flexibility in an optical network for customization of thetransmission and protection of groups of channels.

For example, in some embodiments, the first signal 101 a and the secondsignal 101 b can be delivered by the same transmitter and can besubstantially identical. In this case, the apparatus 100 can function asan optical protection switch. For example, the apparatus 100 can selecteither the first signal 101 a or the second signal 101 b for furtheruse.

In some embodiments, the first optical signal 101 a and the secondsignal 101 b can be different, in which case the apparatus 100 canfunction as a multidirectional multiplexer. In some embodiments, the twooptical signals 101 a and 101 b can have different wavelengths. In someembodiments, the two optical signals 101 a and 101 b can have differentpolarizations. In some embodiments, the two optical signals 101 a and101 b can have different time delays (also referred to as phases).

The reconfigurable optical switch 140 also includes an output port 130,in optical communication with the first switch 120 a and the secondswitch 120 b, to receive possible signal(s) transmitted through thefirst switch 120 a and the second switch 120 b. The sum of possiblesignals transmitted through the two switches 120 a and 120 b forms anoutput signal 102. An optical combiner (not shown) can be used in thereconfigurable optical switch 140 to combine possible signals from thetwo switches 120 a and 120 b.

In some embodiments, the reconfigurable optical switch 140 can also havetransmitting capability by including an input port 150 to receive aninput signal, which is then split into two transmitting paths 160 a and160 b. In these embodiments, the reconfigurable switch 140 isbi-directional.

The first ROADM 110 a and the second ROADM 110 b (collectively referredto as the ROAMDs 110 or ROADM degrees 110) can be based on variousapproaches. In some embodiments, the ROADMs 110 can include wavelengthblocker (WB) type ROADMs. In some embodiments, the ROADMs 110 can bebased on small switch arrays (SSAs). In some embodiments, the ROADMs 110can use wavelength selective switches (WSSs). In some embodiments, theROADMs 110 can be based on optical cross-connect (OXC). For ROADMs basedon SSA and OXC techniques, additional wavelength selection elements canbe included.

The two switches 120 a and 120 b (collectively referred to as switches120) can also include various types of switches to pass/block opticalsignals. In some embodiments, the switches 120 include variable opticalattenuators (VOAs). The VOAs can pass the optical signals 101 a and 101b in the low-loss state and block the optical signals 101 a and 101 b inthe high-loss state. In some embodiments, the attenuation ratio of theVOAs can be greater than 15 dB (e.g., greater than 15 dB, greater than20 dB, greater than 25 dB, greater than 30 dB, greater than 35 dB, orgreater than 40 dB, including any values and sub ranges in between).

In some embodiments, the switches 120 can include electro-opticalswitches, which usually employ one or more electro-optical crystals withvariable refractive index(ices) under an electric field. In someembodiments, the electro-optical crystal can include at least one ofLithium Niobate (LiNbO₃), Lithium Tantalate (LiTaO₃), Lead ZirconateTitanate (Pb(Zr, Ti)O₃), and Lead Lanthanum Zirconate Titanate [(Pb,La)(Zr, Ti)O₃, among others. In some embodiments, the electro-opticalswitch can be based on Mach-Zehnder interferometers, in which an opticalsignal is split into two arms of the interferometers and changing therefractive index in one arm can alter the interference between theoptical signals from the two arms. For example, a constructiveinterference can be configured as the first state to generate an outputsignal substantially identical to the input optical signal, while adestructive interference can be configured as the second state togenerate an output signal with negligible power.

In some embodiments, the switches 120 can include acousto-opticswitches, which use acoustic waves to change the transmission of theswitches. In some embodiments, the switches 120 can includeopto-mechanical switches, which usually redirect an optical signal bymoving bulk fiber optic cable elements by mechanical devices. Forexample, an opto-mechanical switch can use a stepper motor to move amirror that directs the optical signal (light) from the input to thedesired output.

In some embodiments, the switches 120 are controlled manually by a user.In some embodiments, the switches 120 can be controlled by a controller170. The controller 170 in the apparatus 100 can include any suitableprocessor capable of executing computer instructions. Each module in theprocessor can be any combination of hardware-based module (e.g., afield-programmable gate array (FPGA), an application specific integratedcircuit (ASIC), a digital signal processor (DSP) and/or software-basedmodule (e.g., a module of computer code stored in memory and/or executedat the processor) configured to execute a specific function. Theprocessor can be a microcontroller, a FPGA, an ASIC, or any othersuitable processor configured to run and/or execute the modules. Theprocessor and modules of the processor can be configured to collectivelyexecute the methods described herein, and/or to implement theapparatuses described herein.

FIG. 2 shows a schematic of a reconfigurable optical switch 200configured in optical protection mode, according to some embodiments.The reconfigurable optical switch 200 includes a first switch 220 a toreceive a first optical signal 201 a and a second switch 220 b toreceive a second signal 201 b. An output port 230 is in opticalcommunication with both switches 220 a and 220 b to transmit an outputsignal 202, which is the sum of possible signals transmitted through thetwo switches 220 a and 220 b. The reconfigurable optical switch 200 alsoincludes an input port 250 to receive an input optical signal 203 andsplit the input optical signal 203 into two portions 204 a and 204 b,each of which is directed into a corresponding path 260 a and 260 b.

The optical signals 201 a and 201 b can be substantially identical. Insome embodiments, the optical signals 201 a and 201 b include only onespectral component having one wavelength. In some instances, the opticalsignals 201 a and 201 b include two spectral components having twodistinct wavelengths (e.g., λ₁ and λ₂, as illustrated in FIG. 2). Insome instances, the number of spectral components in each optical signal201 a/b can be greater than 2 (e.g., 3 spectral components, 5 spectralcomponents, 10 spectral components, or greater, including any values andsub ranges in between).

In some embodiments, this group of spectral components (also referred toas wavelength carriers) travels together to form a single data flow(also referred to as a super-channel). In some embodiments, the group ofspectral components can be multiplexed into a single fiber. In someembodiments, the group of spectral components can be multiplexed into asemiconductor waveguide or any other suitable guiding structure.

In operation, the beam path including the first switch 220 a can bedesignated as the primary path and the switch 220 a is set in the “pass”state to pass the first optical signal 201 a. The beam path includingthe second switch 220 b can be designated as the secondary path and thesecond switch 220 b is set in the “block” state to block the secondoptical signal 201 b. Therefore, the output signal 202 can besubstantially identical to the first optical signal 201 a.

In the event that a failure is detected in the primary path, theapparatus 200 can close the primary path and use the secondary path totransmit optical signals. In this case, the first switch 220 a isswitched to the “block” state and the second switch 220 b is switched tothe “pass” state. Accordingly, the output signal 202 can besubstantially identical to the second optical signal 201 b.

In some embodiments, the path failure can be determined based on theoverall optical power measured at the output port 230. For example, adetector (not shown) can be disposed at the output port 230 to measurethe amplitude, power, and/or intensity of the output signal 202. Themeasured signal is then transmitted to a controller (not shown) in theapparatus 200. When the measured signal is below a threshold value, thecontroller can determine that a failure in the primary path occurred andswitch the transmission path from the primary path to the secondarypath.

In some embodiments, the path failure can be determined based on theoptical power of one spectral component in the output signal 202. Insome embodiments, the path failure can be determined based on theoptical power of a sub-group of spectral components in the output signal202. In these embodiments, a spectral analyzer (not shown) can bedisposed at the output port 230 to measure the spectral power of theoutput signal 202.

In some embodiments, the path failure can be determined based on thesignal-to-noise ratio (SNR) of the output signal 202. In someembodiments, the path failure can be determined based on the bit errorrate (BER) in the data received at the output port 230. In someembodiments, any of the above mentioned measurements can be performed atthe switches 220 a and/or 220 b to detect path failures.

FIG. 3 shows a schematic of a reconfigurable optical switch 300configured in multi-direction mode, according to some embodiments. Thehardware structure of the reconfigurable optical switch 300 can beidentical to the hardware structure of the reconfigurable optical switch200 shown in FIG. 2, but the switches are configured such that thereconfigurable optical switch 300 functions as a multi-directionalmultiplexer.

The reconfigurable optical switch 300 includes a first switch 320 a toreceive a first optical signal 301 a and a second switch 320 b toreceive a second signal 301 b. An output port 330 is in opticalcommunication with both switches 320 a and 320 b to transmit an outputsignal 302, which is the sum of possible signals transmitted through thetwo switches 320 a and 320 b. The reconfigurable optical switch 300 alsoincludes an input port 350 to receive an input optical signal 303 andsplit the input optical signal 303 into two portions 304 a and 304 b,each of which is directed into a corresponding path 360 a and 360 b.

The switches 320 a and 320 b in the reconfigurable optical switch 300are both set in the “pass” state to pass the corresponding opticalsignal 301 a and 301 b. Accordingly, the output signal 302 is a sum ofthe optical signals 301 a and 301 b. In some embodiments, the firstoptical signal 301 a includes a first spectral component at a firstwavelength λ₁, and the second optical signal 301 b includes a secondspectral component at a second wavelength λ₂ different from the firstwavelength λ₁. Accordingly, the output signal 320 includes two spectralcomponents at wavelengths λ₁ and λ₂. In some embodiments, the outputsignal 302 can be sent to multiple receivers for coherent detection viaa de-multiplexer, such as a passive splitter. FIGS. 2 and 3 illustratethat by simple reconfiguration of the switches (220 a/b and 320 a/b),one can receive channels from multiple directions simultaneously. Thisapproach allows a protection switch to be reconfigured as an element ofa multi-directional mux/demux through software programmability.

In some embodiments, the first optical signal 301 a can include a firstgroup of spectral components at wavelengths λ₁ , λ₂ . . . and λ_(N),where N is the number of spectral components in the first optical signal301 a and is a positive integer. The second optical signal 302 a caninclude a second group of spectral components at wavelengths λ_(N+1),λ_(N+2) . . . and λ_(N+M), where M is the number of spectral componentsin the second optical signal 301 b and is also a positive integer. Insome embodiments, N and M can be identical. In some embodiments, N and Mcan be different. In some embodiments, each wavelength λ_(J), where j=1, 2, . . . N+M is different from another wavelength λ_(i), where i≠j.

In some embodiments, optical signals having multiple spectral componentsare sent to the reconfigurable optical switch 300 and second statemultiplexing can be used to resolve possible wavelength contention. Forexample, a first ROADM (e.g., the ROADM 110 a shown in FIG. 1) can bedisposed before (i.e., upstream) the first switch 320 a and a secondROADM (e.g., the ROADM 110 b shown in FIG. 1) can be disposed before(i.e., upstream) the second switch 320 b. In some embodiments, the firstROADM is configured to pass spectral components at the first wavelengthλ₁ and block other spectral components, while the second ROADM isconfigured to pass spectral components at the second wavelength λ₂ andblock other spectral components. In this manner, the first ROADMgenerates the first optical signal 301 a and the second ROADM generatesthe second optical signal 301 b.

In some embodiments, the first ROADM is configured to pass spectralcomponents at a first group of wavelengths and the second ROADM isconfigured to pass spectral components at a second group of wavelengths.In this case, each of the first optical signal 301 a and the secondoptical signal 301 b can include multiple spectral components, and thereconfigurable optical switch 300 can function as a multi-directionalmultiplexer to multiplex two super channels.

In some embodiments, the transmission section of the reconfigurableoptical switch 300 can be configured to receive the input signal 303including multiple spectral components (e.g., at λ₁ and λ₂, asillustrated in FIG. 3). The input signal 303 is split into two copies,which are directed to the two paths 360 a and 360 b. Second stagemultiplexing, such as ROADMs, can be used to block the spectralcomponent at λ₂ in the first path 360 a and block the spectral componentat λ₁ in the second path 360 b. These two spectral components can thenbe delivered to two different destinations in an optical network.

FIG. 4 shows a schematic of a reconfigurable optical switch 400including four switches 420 a, 420 b, 420 c, and 420 d (collectivelyreferred to as switches 420). A common output port 430 is in opticalcommunication with all the switches 420 to transmit an output signalthat is a sum of possible signals transmitted through the switches 420.The reconfigurable optical switch 400 also includes a transmissionsection that includes an input port 450 and four transmission paths 460a, 460 b, 460 c, and 460 d (collectively referred to as transmissionpaths 460).

In some embodiments, the reconfigurable optical switch 400 can beconfigured as a protection switch and the optical signals received bythe four switches 420 can be substantially identical. In the event thatone optical channel (e.g., the channel including the first switch 420 a)has a failure, the reconfigurable optical switch 400 can select any ofthe remaining three channels for optical communication (e.g., by closingthe first switch 420 a and opening any one of the remaining threeswitches 420 b, 420 c, or 420 d).

In some embodiments, the reconfigurable optical switch 400 can beconfigured as a multi-directional multiplexer. In these embodiments, allswitches 420 are set in the “pass” state to pass the correspondingoptical signals. Therefore, the reconfigurable optical switch 400 canmultiplex optical signals from four directions.

In some embodiments, the reconfigurable optical switch 400 can beconfigured as a hybrid of a protection switch and a multi-directionalmultiplexer. For example, the first switch 420 a and the second switch420 b can receive optical signals that are identical, i.e., A_(in)=B_(in). The third switch 420 c and the fourth switch 420 d can receiveoptical signals that are identical, i.e., C_(in)=D_(in), butA_(in)≠B_(in). In this case, the first switch 420 a and the secondswitch 420 b can collectively function as a first protection switch, andthe third switch 420 c and the fourth switch 420 d can function as asecond protection switch. The four switches 420 then collectivelyfunction as a multi-directional multiplexer to generate an output signalthat is the sum of A_(in)/B_(in) and C_(in)/D_(in).

In FIG. 4, four switches 420 are shown for illustration purposes only.In practice, the number of switches 420 can be less than or greater than4 (e.g., 3 switches, 5 switches, 6 switches, 7 switches, 8 switches, 10switches, 12 switches, or more, including any values and sub ranges inbetween). In some embodiments, the number of switches 420 can be 2 ^(N),where N is a positive integer. For example, the number of switches 420can be 2, 4, 8, 16, 32, 64, or 128.

FIG. 5 shows a schematic of an optical network 500 using reconfigurableoptical switches for optical channel (OCH) protection andmulti-directional multiplexing, according to some embodiments. Theoptical network 500 includes a first node 510 and a second node 520communicating with each other via two optical channels 530 a and 530 b.The first node 510 includes a transceiver 512 to transmit an opticalsignal. The optical signal is sent to a reconfigurable optical switch514, which splits the optical signal into two portions: the firstportion is delivered to a first mux/demux 516 a connected to the firstpath 530 a, and the second portion is delivered to a second mux/demux516 b connected to the second path 530 b. The second node 520 includes afirst mux/demux 526 a connected to the first path 530 a and a secondmux/demux 526 b connected to the second path 530 b. A secondreconfigurable optical switch 524 is coupled to both mux/demux 526 a and526 b and transmits/receives signals from a transceiver 522. Thereconfigurable optical switches 514 and 524 can be substantiallyidentical to any of the reconfigurable optical switches described hereinand detailed description of them are not repeated.

The transceivers 512 and 522 can include one or more types oftransmitters. In some embodiments, the transmitter can include acoherent transmitter. In some embodiments, the transmitter can include aC-form pluggable generation (CFP) transmitter. In some embodiments, thetransmitter can include a CFP4 transmitter, which can be coherent ornon-coherent. In some embodiments, the transmitter can include a C-formpluggable generation 2—analog coherent optics (CFP2-ACO) transmitterthat is coupled with a digital signal processor (DSP) chip through apluggable interface.

In some embodiments, the transmitter can include a coherentin-phase/quadrature transmitter integrated together with a DSP within aphysical module. In some embodiments, the transmitter can include aC-form pluggable generation—digital coherent optics (CFP-DCO)transmitter integrated with a DSP and an optical front end. In someembodiments, the transmitter can include a Quad Small Form-factorPluggable (QSFP) transmitter. In some embodiments, the transmitter caninclude a QSFP28 transmitter. These transmitters can be coherent orincoherent.

In operation, the communication between the first node 510 and thesecond node 520 is bi-directional. The receiving ends (also referred toas the tail-end) of the reconfigurable optical switches 514 and 524include two 1×1 switches. In some embodiments, the reconfigurableoptical switches 514 and 524 can be employed for path protection. Inthese embodiments, one switch in each reconfigurable optical switch (514and 524) is in the pass state and the other switch is in the block stateto allow communication between the two nodes 510 and 520 via either thefirst path 530 a or the second path 530 b.

In some embodiments, both switches in each reconfigurable optical switch(514 and 524) are in the pass state to collect signals from both paths530 a and 530 b. In some embodiments, one reconfigurable optical switch(e.g., 514) can be employed for path protection for communication fromthe second node 520 to the first node 510, while the otherreconfigurable optical switch (e.g., 524) can be employed formulti-directional multiplexing for communication on the reversedirection, i.e., from the first node 510 to the second node 520.Although one transceiver (512 and 522) is shown on each node (510 and520, respectively), in practice, each node 510 and 520 can includemultiple transceivers. A power splitter can be disposed between thereconfigurable optical switch (514 and 524) and the transceivers (512and 522) to split the optical signals to each transceiver.

FIG. 6 shows a schematic of an optical network 600 using reconfigurableoptical switches for optical multiplexing section (OMS) protection andmulti-directional multiplexing, according to some embodiments. Theoptical network 600 includes a first node 610 and a second node 620 incommunication with each other via two paths 630 a and 630 b. Thedescription below uses the communication from the first node 610 to thesecond node 620 for illustration purposes, and the communication on thereverse direction (i.e. from the second node 620 to the first node 610)can be substantially symmetric.

The first node 610 includes a transceiver 612 to provide (or receive)optical signals that are sent to a mux/demux 616. A reconfigurableoptical switch 614 receives the optical signals from the mux/demux 616and splits the optical signals into the first path 630 a and 630 b. Thesecond node 620 also includes a reconfigurable optical switch 626connected to both paths 630 a and 630 b to collect signals transmittedfrom these two paths 630 a and 630 b. A mux/demux 624 is employed toreceive signals from the reconfigurable optical switch 626 and send thesignals to a transceiver 622.

In some embodiments, the reconfigurable optical switch 626 can beemployed for path protection per multiplexing (e.g., one switch in thepass state and the other switch in the block state). In someembodiments, the reconfigurable optical switch 626 can be employed formulti-directional multiplexing (e.g., both switches are in the passstate). In some embodiments, a controller (not shown in FIG. 6) can beused to switch between these two modes remotely, without changing anyhardware components in the optical network. Although one transceiver(612 and 622) is shown on each node (610 and 620, respectively), inpractice, each node 610 and 620 can include multiple transceivers. Apower splitter can be disposed between the reconfigurable optical switch(614 and 624) and the transceivers (612 and 622) to split the opticalsignals to each transceiver.

FIG. 7 shows a schematic of an optical network 700 including groupmultiplexing and using a reconfigurable optical switch for pathprotection and multi-directional multiplexing. The network 700 includesa first node 710, a second node 720, and multiple add/drop stages 730 a,730 b, and 730 c connected between the first node 710 and the secondnode 720. The description herein uses the second stage 730 b forillustration purposes, but other stages (e.g., 730 a and 730 c) can havesimilar structures and functions.

The add/drop stage 730 b includes a pair of transceivers 732 and 734(both can be bi-directional with add/drop functions), a mux/demux 736coupled to the transceivers 732 and 734, and a reconfigurable opticalswitch 740 connected between the mux/demux 736 and the two nodes 710 and720. The reconfigurable optical switch 740 can be substantiallyidentical to any of the reconfigurable optical switches described aboveand detailed description is not repeated.

In some embodiments, the reconfigurable optical switch 740 can have onlyone of the two switches in the pass state and the other switch in theblock state. In this manner, the second stage 730 b can receive signalsfrom either the first node 710 or the second node 720. In someembodiments, the reconfigurable optical switch 740 can have bothswitches in the pass state to receive signal from both nodes 710 and720, i.e., multi-directional multiplexing.

FIG. 8 shows a schematic of an optical network 800 including areconfigurable optical switch for path protection, according to someembodiments. The optical network 800 includes a first node 810 and asecond node 820 in communication with each other via two possible paths830 a and 830 b. The following description uses the communication fromthe first node 810 to the second node 820 for illustration purposes, andthe communication on the reverse direction (i.e., from the second node820 to the first node 810) can be substantially symmetric.

The first node 810 includes a pair of transceivers 812 a and 812 b todeliver a first spectral component at a first wavelength λ₁ and a secondspectral component at a second optical signal λ₂, respectively. The twospectral components are combined using a combiner 814 to form a singleoptical signal, referred to as the transmission signal. The first node810 also includes a reconfigurable optical switch 816 to split thetransmission signal into a first portion and a second portion, each ofwhich include both spectral components at λ₁ and λ₂. The first portionis sent to a first ROADM 818 a, which in turn delivers the first portionto the first path 830 a. The second portion is sent to a second ROADM818 b, which in turn delivers the second portion to the second path 830b.

On the receiving end, the second node 820 includes a first ROADM 828 ato receive the first portion of the transmission signal from the firstpath 830 a and a second ROADM 828 b to receive the second portion of thetransmission signal from the second path 830 b. A reconfigurable opticalswitch 826 is connected to both ROADMs 828 a and 828 b. Morespecifically, the reconfigurable optical switch 826 incudes a firstswitch connected to the first ROADM 828 a and a second switch connectedto the second ROADM 828 b. In some embodiments, a splitter 824 isemployed in the second node 820 to direct the first spectral componentat λ₁ to a first transceiver 822 a and direct the second spectralcomponent at λ₂ to a second transceiver 822 b. In some embodiments, thesplitter 824 is configured to direct both spectral components at λ₁ andλ₂ to each transceiver 822 a and 822 b (as shown in FIG. 8).

In operation, one switch in the reconfigurable optical switch 826 is inthe pass state and the other switch in the reconfigurable optical switch826 is in the block state for path protection. For example, the topswitch in the reconfigurable optical switch 826 can be initially set inthe pass state to allow communication between the two nodes 810 and 820via the first path 830 a. In the event that the first path 830 fails,the system 800 can then use the second path 830 b for communication byswitching the top switch in the reconfigurable optical switch 826 intothe block state and switching the bottom switch in the reconfigurableoptical switch 826 into the pass state. In this manner, both wavelengthsλ₁ and λ₁ are protected.

FIG. 9 shows a schematic of an optical network 900 including areconfigurable optical switch for multi-directional multiplexing,according to some embodiments. The optical network 900 includes a firstnode 910, a second node 920, and a third node 930. For illustrationpurposes only, FIG. 9 shows only the first path 940 a between the firstnode 910 and the third node 930, and the second path 940 b between thesecond node 920 and the third node 930. Other paths are also possible(e.g., a path between the first node 910 and the second node 920).

The first node 910 includes a transceiver 912 to deliver a firstspectral component at λ₁ and a reconfigurable optical switch 916 tosplit the first spectral component into a first portion and a secondportion. The first portion is sent to a first ROADM 918 a and the secondportion is sent to a second ROADM 918 b that is connected to the firstpath 940 a toward the third node 930. An optional combiner 914 is alsoincluded in the first node 910 to combine spectral components whenmultiple transceivers are used.

The second node 920 includes a transceiver 922 to deliver a secondspectral component at λ₂ and a reconfigurable optical switch 926 tosplit the second spectral component into a first portion and a secondportion. The first portion is sent to a first ROADM 928 a and the secondportion is sent to a second ROADM 928 b that is connected to the secondpath 940 b toward the third node 930. An optional combiner 924 is alsoincluded in the second node 920 to combine spectral components whenmultiple transceivers are used.

The third node 930 includes a first ROADM 938 a connected to the firstpath 940 a to receive the first spectral component at λ₁ and a secondROADM 938 b connected to the second path 940 b to receive the secondspectral component at λ₂. The first ROADM 938 a is configured to passspectral components at λ₁ and block spectral components at otherwavelengths (e.g., λ₂) to avoid interference. Similarly, the secondROADM 938 b is configured to pass spectral component at λ₂ and blockspectral components at other wavelengths (e.g., λ₁) to avoidinterference.

The third node 930 also includes a reconfigurable optical switch 936connected to the two ROADMs 938 a and 938 b to combine the firstspectral component at λ₁ with the second spectral component at λ₂. Thecombined signal is delivered to a splitter 934, which directs the firstspectral component to a first transceiver 932 a operating at λ₁ anddirects the second spectral component to a second transceiver 932 boperating at λ₂.

FIGS. 10A and 10B each illustrate a schematic of an optical network 1000having reconfigurability between path protection and multi-directionalmultiplexing of an optical network, according to some embodiments. Asshown in FIG. 10A, the optical network 1000 includes a first node 1010,a second node 1020, and a third node 1030. The first node 1010 includesa pair of transceivers 1012 a operating at λ₁ and 1012 b operating atλ₂. A combiner 1014 is used to combine the two spectral components at λ₁and λ₂. The first node 1010 also includes a reconfigurable opticalswitch 1016 to split the combined signal into a first portion directedto a first ROADM 1018 a and a second portion directed to a second ROADM1018 b. The first ROADM 1018 a is connected to a first path 1040 atoward the second node 1020 and the second ROADM 1018 b is connected toa second path 1040 b toward the third node 1030.

The second node 1020 includes a pair of transceivers 1022 a operating atλ₁ and 1022 b operating at λ₃, respectively. A combiner 1024 is used tocombine the two spectral components at λ₁ and λ₃. The second node 1020also includes a reconfigurable optical switch 1026 to split the combinedsignal into a first portion directed to a first ROADM 1028 a and asecond portion directed to a second ROADM 1028 b. The first ROADM 1028 ais connected to the first path 1040 a toward the first node 1010 and thesecond ROADM 1028 b is connected to a third path 1040 c toward the thirdnode 1030.

The third node 1030 includes a pair of transceivers 1032 a operating atλ₂ and 1032 b operating at λ₃. A combiner 1034 is used to combine thetwo spectral components at λ₂ and λ₃. The first node 1030 also includesa reconfigurable optical switch 1036 to split the combined signal into afirst portion directed to a first ROADM 1038 a and a second portiondirected to a second ROADM 1038 b. The first ROADM 1038 a is connectedto the second path 1040 b toward the first node 1010 and the secondROADM 1038 b is connected to the third path 1040 c toward the secondnode 1020.

In FIG. 10A, the network 1000 operates at the broadcast mode. In thismode, the ROADM 1018 a in the first node 1010 is configured to pass thespectral component at λ₁ (and block the spectral component at λ₂ ).Therefore, the communication between the first node 1010 and the secondnode 1020 via the first path 1040 a is at λ₁. The ROADM 1018 b in thefirst node is configured to pass the spectral component at λ₂ (and blockthe spectral component at λ₁ ). Therefore, the communication between thefirst node 1010 and the third node 1030 is at λ₂. In the second node1020, the ROADM 1028 b is configured to pass the spectral component atλ₃ (and block the spectral component at λ₁ ). Accordingly, thecommunication between the second node 1020 and the third node 1030 is atλ₃.

From the perspective of the third node 1030, the reconfiguration opticalswitch 1036 is configured to receive the spectral component at λ₂ fromthe first node 1010 and receive the spectral component at λ₃ from thesecond node 1020. These two spectral components are combined by thereconfigurable optical switch 1036 and the combined signal can be thenspectrally split by the combiner 1034 (now functioning as a splitter).The spectral component at λ₂ can be directed to the transceiver 1032 aand the spectral component at λ₃ can be directed to the transceiver 1032b.

In some embodiments, the combined signal after the reconfigurableoptical switch 1036 can be directed to both transceivers 1032 a and 1032b without spectral separation. The transceivers 1032 a and 1032 b caninclude demultiplexer(s) or other devices to separate the spectralcomponents from each other.

From the perspective of the second node 1020, the reconfigurable opticalswitch 1026 receives the spectral component at λ₁ from the first nodeand receives the spectral component at λ₃ from the third node 1030. Inthe first node 1010, the reconfigurable optical switch 1016 receives thespectral component at λ₁ from the second node 1020 and receives thespectral component at λ₂ from the third node 1030. Therefore, each node(1010, 1020, and 1030) is operating in multi-directional multiplexingmode to receive different spectral components from the other two nodes.

In FIG. 10B, the network 1000 operates at the path protection mode. Inthis mode, the third node 1030 is bypassed (it is shown partiallyvisible for illustration purposes), and the two ROADMs 1038 a and 1038 bin the third node 1030 can function as a bridge to connect the paths1040 b and 1040 c into a continuous one, referred to as 1040 d in thissection.

In optical protection mode, the ROADMs 1018 a and 1018 b in the firstnode are configured to pass spectral components at both λ₁ and λ₂. Thetwo transceivers 1022 a and 1022 b in the second node 1020 are alsoconfigured to operate at λ₁ and λ₂, respectively. In addition, the twoROADMs 1028 a and 1028 b are configured to transmit spectral componentsat both λ₁ and λ₂. Therefore, signals having spectral components at λ₁and λ₂ can be communicated between the first node 1010 and the secondnode 1020 via either the first path 1040 a or the second path 1040 d.The reconfigurable optical switch 1026 can select which path to use forthe traffic from the first node 1010 to the second node 1020, and thereconfigurable optical switch 1016 in the first node can select whichpath to use for the traffic along the reverse direction, i.e., from thesecond node 1020 to the first node 1010.

For example, the reconfigurable optical switch 1026 can have its topswitch in the pass state and the bottom switch in the block state tochoose the first path 1040 a for receiving communication from the firstnode 1010. Alternatively, the reconfigurable optical switch 1026 canhave its top switch in the block state and the bottom switch in the passstate to choose the second path 1040 d for receiving communication fromthe first node 1010

FIGS. 10A and 10B illustrate that reconfigurability between opticalprotection mode and broadcast mode can be readily achieved by changingthe status of the reconfigurable optical switches. In other words, thereconfiguration does not change any of the hardware component (e.g.,ROAMDs, switches, combiners, and/or transceivers) in the optical network1000. The broadcast mode allows for a more efficient use of themultiplex ports in the network 1000 by allowing common equipment to bedeployed and then application determined by later configuration orreconfiguration. In contrast, known methods to switch between opticalprotection and broadcasting usually include physical changes of theoptical path in the network (e.g., inserting or removing an opticalprotection switch from the path). These changes are typically not atouch-less operation and therefore can be much more cumbersome toachieve, with greater potential to cause errors during thereconfiguration.

FIG. 11 illustrates a method 1100 of optical communication, according tosome embodiments. The method 1100 includes, at 1110, receiving a firstoptical signal from a first reconfigurable optical add/drop multiplexer(ROADM). The first optical signal is then transmitted to a first switchin optical communication with the first ROADM and switchable between afirst state and a second state, at 1120. The first switch is configuredto transmit the first optical signal at the first state and block thefirst optical signal at the second state. The method 1100 also includesreceiving a second optical signal from a second ROADM at 1130 andtransmitting the second optical signal to a second switch at 1140. Thesecond switch is in optical communication with the second ROADM andswitchable between the first state and the second state. The secondswitch is configured to transmit the second optical signal at the firststate and block the second optical signal at the second state. At 1150,an output signal is generated by combining possible optical signalstransmitted through the first switch and the second switch.

In some embodiments, the first switch and the second switch include avariable optical attenuator (VOA). The low-loss state of the VOA can beused as the first state to pass optical signals and the high-loss stateof the VOA can be used as the second state to block optical signals.

In some embodiments, the first ROADM is configured to transmit a firstspectral component at a first wavelength and block spectral componentsat other wavelengths. The second ROADM is configured to transmit asecond spectral component at a second wavelength and block spectralcomponents at other wavelengths. The first wavelength and the secondwavelength are different. In these embodiments, the output signal can begenerated by combining the first spectral component and the secondspectral component. In some embodiments, the first spectral componentand the second spectral component are delivered from differentdirections and the method 1100 can be employed for multi-directionalmultiplexing.

In some embodiments, the first ROADM is configured to transmit a firstgroup of spectral component at a first group of wavelengths and blockspectral components at other wavelengths. The second ROADM is configuredto transmit a second group of spectral components at a second group ofwavelengths and block spectral components at other wavelengths. Eachgroup of spectral components can be multiplexed into a single fiber orwaveguide to travel together and form a super channel for datacommunication.

In some embodiments, the output signal includes multiple spectralcomponents, and the method 1100 further includes demultiplexing theoutput signal and directing each spectral component into a correspondingreceiver. In some embodiments, a separate demultiplexer can be used todemultiplex the output signal. In some embodiments, optical splittersare used to demultiplex the output signal.

In some embodiments, the method 1100 further includes detecting at leastone attribute of the first optical signal. In response to the attributeof the first optical signal being unsatisfactory (e.g., less than athreshold value), the first switch is switched to the second state toblock the first optical signal and the second switch is switched to thefirst state to transmit the second optical signal. In some embodiments,the attribute of the first optical signal includes the overall amplitude(or power) of the first optical signal. In some embodiments, theattribute of the first optical signal includes the amplitude (or power)of one spectral component in the first optical signal. In someembodiments, the attribute of the first optical signal includes thesignal-to-noise ratio (SNR) of the first optical signal. In someembodiments, the attribute of the first optical signal includes the biterror rate (BER) of the first optical signal.

In some embodiments, the method 1100 further includes switching betweena first operation mode and a second operation mode. In the firstoperation mode, the first switch is configured in the first state andthe second switch is configured in the second state for path protection.In the second operation mode, both the first switch and the secondswitch are configured in the first state for multi-directionalmultiplexing. The switching between these two modes can be achievedremotely by a controller.

In some embodiments, the method 1100 further includes receiving a thirdoptical signal from a third ROADM and transmitting the third opticalsignal to a third switch in optical communication with the third ROADMand switchable between the first state and the second state. The thirdswitch is configured to transmit the third optical signal at the firststate and block the third optical signal at the second state. In theseembodiments, the output signal is generated by combining possiblesignals transmitted through the first switch, the second switch, and thethird switch.

While various embodiments have been described and illustrated herein, avariety of other means and/or structures for performing the functionand/or obtaining the results and/or one or more of the advantagesdescribed herein, and each of such variations and/or modifications arepossible. More generally, all parameters, dimensions, materials, andconfigurations described herein are meant to be examples and that theactual parameters, dimensions, materials, and/or configurations willdepend upon the specific application or applications for which thedisclosure is used. It is to be understood that the foregoingembodiments are presented by way of example only and that otherembodiments may be practiced otherwise than as specifically describedand claimed. Embodiments of the present disclosure are directed to eachindividual feature, system, article, material, kit, and/or methoddescribed herein. In addition, any combination of two or more suchfeatures, systems, articles, materials, kits, and/or methods, if suchfeatures, systems, articles, materials, kits, and/or methods are notmutually inconsistent, is included within the inventive scope of thepresent disclosure.

Also, various inventive concepts may be embodied as one or more methods,of which an example has been provided. The acts performed as part of themethod may be ordered in any suitable way. Accordingly, embodiments maybe constructed in which acts are performed in an order different thanillustrated, which may include performing some acts simultaneously, eventhough shown as sequential acts in illustrative embodiments.

All definitions, as defined and used herein, should be understood tocontrol over dictionary definitions, definitions in documentsincorporated by reference, and/or ordinary meanings of the definedterms.

As used herein, a “module” can be, for example, any assembly and/or setof operatively-coupled electrical components associated with performinga specific function, and can include, for example, a memory, aprocessor, electrical traces, optical connectors, software (stored andexecuting in hardware) and/or the like.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Multiple elements listed with“and/or” should be construed in the same fashion, i.e., “one or more” ofthe elements so conjoined. Other elements may optionally be presentother than the elements specifically identified by the “and/or” clause,whether related or unrelated to those elements specifically identified.Thus, as a non-limiting example, a reference to “A and/or B”, when usedin conjunction with open-ended language such as “comprising” can refer,in one embodiment, to A only (optionally including elements other thanB); in another embodiment, to B only (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of,” or, when usedin the claims, “consisting of,” will refer to the inclusion of exactlyone element of a number or list of elements. In general, the term “or”as used herein shall only be interpreted as indicating exclusivealternatives (i.e. “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of,” or“exactly one of.” “Consisting essentially of,” when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” “composed of,” and the like are tobe understood to be open-ended, i.e., to mean including but not limitedto. Only the transitional phrases “consisting of” and “consistingessentially of” shall be closed or semi-closed transitional phrases,respectively, as set forth in the United States Patent Office Manual ofPatent Examining Procedures, Section 2111.03.

What is claimed is:
 1. An optical network, comprising: a first nodeincluding: a first transceiver configured to transmit a first opticalsignal; a first reconfigurable optical add/drop multiplexer (ROADM)operatively coupled to the first transceiver; a first switch disposedbetween the first ROADM and the first transceiver; a second ROADMoperatively coupled to the first transceiver; and a second switchdisposed between the second ROADM and the first transceiver; a secondnode including: a second transceiver configured to transmit a secondoptical signal; a third ROADM operatively coupled to the secondtransceiver and configured to receive the first optical signal from thefirst node; a third switch disposed between the third ROADM and thesecond transceiver; a fourth ROADM operatively coupled to the secondtransceiver; and a fourth switch disposed between the fourth ROADM andthe second transceiver; a third node including: a third transceiverconfigured to transmit a third optical signal; a fifth ROADM operativelycoupled to the third transceiver and configured to receive the firstoptical signal from the first node; a fifth switch disposed between thefifth ROADM and the third transceiver; a sixth ROADM operatively coupledto the third transceiver and configured to receive the second opticalsignal from the second node; and a sixth switch disposed between thesixth ROADM and the third transceiver; and a controller, operativelycoupled to the first node, the second node, and the third node, tocontrol the first switch, the second switch, the third switch, thefourth switch, the fifth switch, and the sixth switch.
 2. The opticalnetwork of claim 1, wherein: the first transceiver is configured totransmit a first portion of the first optical signal to the second nodevia a first optical channel and transmit a second portion of the firstoptical signal to the second node via a second optical channel, thefirst optical signal comprising a first spectral component at a firstwavelength and a second spectral component at a second wavelength, andthe controller opens the third switch in the second node to receive thefirst portion of the first optical signal via the first optical channeland closes the fourth switch in the second node to block the secondportion of the first optical signal.
 3. The optical network of claim 1,wherein: the first transceiver is configured to transmit the firstoptical signal to the third node via a first optical channel, the firstoptical signal comprising a first spectral component at a firstwavelength and a second spectral component at a second wavelength, thesecond ROADM in the first node is configured to transmit the secondspectral component at the second wavelength and block the first spectralcomponent at the first wavelength, the second transceiver is configuredto transmit the second optical signal to the third node via a secondoptical channel, the second optical signal comprising a third spectralcomponent at a third wavelength and a fourth spectral component at thefirst wavelength, the fourth ROADM in the second node is configured totransmit the third spectral component at the third wavelength and blockthe fourth spectral component at the first wavelength, and thecontrollers opens the fifth switch and the sixth switch in the thirdnode to receive the second spectral component from the first node andthe third spectral component from the second node.
 4. The opticalnetwork of claim 1, wherein at least one of the first switch or thesecond switch includes a variable optical attenuator (VOA).
 5. Theoptical network of claim 1, wherein at least one of the first switch orthe second switch includes a 1×1 opto-mechanical switch.
 6. The opticalnetwork of claim 1, wherein: the first transceiver is configured totransmit the first optical signal at a first wavelength to the thirdnode, the second transceiver is configured to transmit the secondoptical signal at a second wavelength to the third node, and the thirdnode further includes a fourth transceiver, the third transceiverconfigured to receive the first optical signal from the firsttransceiver, and the fourth transceiver configured to receive the secondoptical signal from the second transceiver.
 7. The optical network ofclaim 1, the first transceiver is configured to transmit the firstoptical signal at a first wavelength to the third node, the secondtransceiver is configured to transmit the second optical signal at asecond wavelength to the third node, and the third node furtherincludes: a fourth transceiver; and a splitter, the fifth switchconfigured to transmit the first optical signal to the splitter, thesixth switch configured to transmit the second optical signal to thesplitter, the splitter configured to direct the first optical signal tothe third transceiver and direct the second optical signal to the fourthtransceiver.
 8. The optical network of claim 1, wherein: the firsttransceiver is configured to transmit the first optical signal at afirst wavelength to the third node, the second transceiver is configuredto transmit the second optical signal at a second wavelength to thethird node, the fifth ROADM in the third node is configured to pass thefirst optical signal at the first wavelength and block optical signalsat other wavelengths, the sixth ROADM in the third node is configured topass the second optical signal at the second wavelength and blockoptical signals at other wavelength, and the third node further includesa fourth transceiver, the third transceiver configured to receive thefirst optical signal from the first transceiver, and the fourthtransceiver configured to receive the second optical signal from thesecond transceiver.
 9. An optical network, comprising: a first nodecomprising: a first transceiver to transmit a first optical signal at afirst wavelength; a second transceiver to transmit a second opticalsignal at a second wavelength; a first reconfigurable optical add/dropmultiplexer (ROADM) operatively coupled to the first transceiver and thesecond transceiver; a first switch disposed between the first ROADM andthe first transceiver; a second ROADM operatively coupled to the firsttransceiver and the second transceiver; and a second switch disposedbetween the second ROADM and the first transceiver; a second nodecomprising: a third transceiver configured to transmit a third opticalsignal at a third wavelength; a fourth transceiver configured totransmit a fourth optical signal at the first wavelength; a third ROADMoperatively coupled to the third transceiver and the fourth transceiver;a third switch disposed between the third ROADM and the thirdtransceiver; a fourth ROADM operatively coupled to the third transceiverand the fourth transceiver; and a fourth switch disposed between thefourth ROADM and the third transceiver; a third node comprising: a fifthtransceiver; a sixth transceiver a fifth ROADM operatively coupled tothe fifth transceiver and the sixth transceiver; a fifth switch disposedbetween the fifth ROADM and the fifth transceiver; a sixth ROADMoperatively coupled to the fifth transceiver and the sixth transceiver;and a sixth switch disposed between the sixth ROADM and the fifthtransceiver; and a controller, operatively coupled to the first node,the second node, and the third node, to control the first switch, thesecond switch, the third switch, the fourth switch, the fifth switch,and the sixth switch.
 10. The optical network of claim 9, wherein atleast one of the first switch or the second switch includes a variableoptical attenuator (VOA).
 11. The optical network of claim 9, wherein atleast one of the first switch or the second switch includes a 1×1opto-mechanical switch.
 12. The optical network of claim 9, wherein: thecontroller is configured to switch the optical network between abroadcast mode and a path protection mode, in the broadcast mode: thesecond ROADM in the first node is configured to transmit the secondoptical signal at the second wavelength and block the first opticalsignal at the first wavelength, the fourth ROADM in the second node isconfigured to transmit the third optical signal at the third wavelengthand block the fourth optical signal at the first wavelength, the fifthROADM in the third node is configured to receive the second optical fromthe first node, and the six ROADM in the third node is configured toreceive the third optical signal from the second node, in the pathprotection mode: the first ROADM in the first node is configured totransmit the first optical signal and the second optical signal to thethird ROADM in the second node via a first optical path, the secondROADM in the first node is configured to transmit the first opticalsignal and the second optical to the fourth ROADM in the second node viaa second optical path, the second optical path further including thefifth ROADM and the sixth ROADM in the third node.
 13. The opticalnetwork of claim 9, wherein: the first ROADM in the first node isconfigured to transmit the first optical signal and the second opticalsignal to the third ROADM in the second node via a first optical path,the second ROADM in the first node is configured to transmit the firstoptical signal and the second optical to the fourth ROADM in the secondnode via a second optical path, the second optical path furtherincluding the fifth ROADM and the sixth ROADM in the third node, and thecontroller is configured to open the third switch in the second node andclose the fourth switch in the second node so as to cause the secondnode to receive the first optical signal and the second optical signalfrom the first optical path.
 14. The optical network of claim 9,wherein: the second ROADM in the first node is configured to transmitthe second optical signal at the second wavelength and block the firstoptical signal at the first wavelength, the fourth ROADM in the secondnode is configured to transmit the third optical signal at the thirdwavelength and block the fourth optical signal at the first wavelength,the fifth ROADM in the third node is configured to receive the secondoptical from the first node, and the six ROADM in the third node isconfigured to receive the third optical signal from the second node, 15.The optical network of claim 9, wherein: the first ROADM in the firstnode is configured to transmit the first optical signal at the firstwavelength to the third ROADM in the second node and block opticalsignals at other wavelengths, the second ROADM in the first node isconfigured to transmit the second optical signal at the secondwavelength to the fifth ROADM in the third node and block the firstoptical signal at the first wavelength, the third ROADM in the secondnode is configured to transmit the fourth optical signal at the firstwavelength to the first ROADM in the first node, the fourth ROADM in thesecond node is configured to transmit the third optical signal at thethird wavelength to the sixth ROADM in the third node and block thefourth optical signal at the first wavelength, the fifth ROADM in thethird node is configured to receive the second optical from the firstnode, and the six ROADM in the third node is configured to receive thethird optical signal from the second node.